Giant takes place on a scorching summer’s day in 1983, in an elegant, ramshackle English country home. Roald Dahl, the world-famous children’s author, is in a terrible mood. His body is wracked by pain, his new book, The Witches, is about to be released, and a public outcry about his recent book review—a coruscating critique of Israel’s siege of Beirut the year before, melded with antisemitic stereotypes—hangs in the air. His fiancée and British…